Phase winding detectors are known in which an AC output signal of the phase winding is detected by the use of a rectifying diode. However, such detectors are not suitable for detecting very low magnitude AC output signals since the AC signal generally must exceed the diode bias threshold in order to achieve detection. In addition, such detectors may have to be used with a DC blocking capacitor of substantial magnitude if the AC signal is superimposed on a DC bias, particularly if the DC bias may vary over time.
Some alternator charging systems detect when the alternator is rotating by monitoring the magnitude of a single output phase winding of the alternator. Since the alternator output may be superimposed on a DC bias, a DC blocking capacitor is utilized to implement detection of small magnitude phase winding signals during start up conditions during which field current excitation for the alternator has not yet been provided. The output of the phase winding detection is then utilized, in some alternator charging systems, to control the switching of operative power to a charging system voltage regulator which will then in turn provide field coil excitation. Since it is necessary to detect the output of an alternator phase winding prior to the application of field coil excitation, it is necessary that the phase winding detector be able to monitor and detect very low magnitude signals. This essentially precludes the use of a detection diode. Also, since preferably it is desirable to utilize as few components as possible, outside of a voltage regulator provided as an integrated circuit (IC), typically it is not desirable to use a large DC blocking capacitor for implementing the function of detecting the output of the alternator. Some prior alternator charging systems have proposed monitoring two phase winding outputs of the alternator and essentially comparing them to arrive at a phase winding detection output without the use of a DC blocking capacitor. However, such systems generally require substantial additional circuitry in addition to the voltage regulator IC or they require connecting each of the two phase windings to a separate input pin of the voltage regulator. The providing of an additional input pin to an integrated circuit voltage regulator is also undesirable.
What is needed is an improved phase winding detector that can be used for detecting alternator rotation. This detector should be able to monitor and detect the output of a single phase winding of the alternator without the use of a large magnitude DC blocking capacitor. The detector should also have the ability to detect very low magnitudes of phase winding output signals and therefore implement such detection without the use of a rectifier diode for rectifying the output of the phase winding.
Phase winding detectors for alternator rotation detection can be used in alternator charging systems in which typically the voltage coupled to the voltage regulator through a charging lamp is normally utilized to control the application of battery power to the voltage regulator. The voltage regulator in such systems also typically will control the drive excitation for the charging indicator lamp such that upon detection of a significant output from the alternator windings, drive excitation through the lamp is halted and the lamp is therefore turned off. In such systems, there is a substantial problem if the lamp is burned out and therefore cannot supply a switching signal to the regulator to indicate that battery power should be applied to the regulator to enable it to supply field coil excitation. Battery power is not always applied to the regulator to generate field coil excitation so as to minimize battery current drain. In such systems, some form of alternator rotation detector is utilized to control the application of battery power to the regulator in response to detecting at least a very low level output of the alternator windings which indicates that the alternator is rotating. However, as noted above, preferably such an alternator rotation detector should have no rectifier diode so that it will be able to sense very low magnitudes of the alternator output phase winding. Also, the detector should function without the use of a large magnitude DC blocking capacitor which therefore cannot be provided as part of an integrated circuit voltage regulator. In addition, the detection of alternator rotation should be implemented by providing no more than one phase winding monitoring input to detection circuitry which is provided as part of a voltage regulator integrated circuit.